The use of mobile communications networks has increased over the last decade. Operators of the mobile communications networks have increased the number of base transceiver stations in order to meet an increased demand for service by users of the mobile communications networks. The operators of the mobile communications network wish to reduce the running costs of the base transceiver station.
Nowadays active antenna arrays are used in the field of mobile communications systems in order to reduce power transmitted to a handset of a customer and thereby increase the efficiency of the base transceiver station, i.e. the radio station. The radio station typically comprises a plurality of antenna elements, i.e. an antenna array adapted for transceiving a payload signal. Typically the radio station comprises a plurality of transmit paths and receive paths. Each of the transmit paths and receive paths are terminated by one of the antenna elements. The plurality of the antenna elements used in the radio station typically allows steering of a beam transmitted by the antenna array. The steering of the beam includes but is not limited to at least one of: detection of direction of arrival (DOA), beam forming, down tilting and beam diversity. These techniques of beam steering are well-known in the art.
The active antenna arrays typically used in the mobile communications network are uniform linear arrays comprising a vertical column of pairs of antenna array elements. The active antenna array or active antenna system is typically mounted on a mast or tower. The active antenna array is coupled to the base transceiver station (BTS) by means of a fibre optics cable and a power cable. The base transceiver station is coupled to a fixed line telecommunications network operated by one or more operators.
Equipment at the base of the mast as well as the active antenna array mounted on the mast is configured to transmit and receive radio signal within limits set by communication standards.
The code sharing and time division strategies as well as the beam steering rely on the radio station and the active antenna array to transmit and receive within limits set by communication standards. The communications standards typically provide a plurality of channels or frequency bands useable for an uplink communication from the handset to the radio station as well as for a downlink communication from the radio station to the subscriber device.
For example, the communication standard “Global System for Mobile Communications (GSM)” for mobile communications uses different frequencies in different regions. In North America, GSM operates on the primary mobile communication bands 850 MHz and 1900 MHz. In Europe, Middle East and Asia most of the providers use 900 MHz and 1800 MHz bands. Other examples are the UMTS standard or long term evolution (LTE) at 700 MHz (US) or 800 MHz (EU).
As technology evolves, the operators have expressed a desire for an active antenna array which is as cost-effective as possible. The side lobe suppression should be maximized without significant increase of antenna size and cost, and without significantly sacrificing the tilt range of the antenna.